The following references will serve as background art for the present invention:
U.S. Pat. No. 3,154,495, Robson et al., issued Oct. 22, 1964, discloses articles comprising enveloped granular and very small tableted hypochlorite materials. British Pat. No. 3,349, Lees, issued Feb. 20, 1892, discloses a disinfecting apparatus using a wire gauze filter means to contain solids.
A partially dissolving cake is disclosed in commonly owned U.S. Pat. No. 4,281,421, Nyquist, Kitko and Stradling, issued Aug. 4, 1981. The partially insoluble cake comprising hypochlorite and metasilicate salts forms an insoluble shell upon use. In one execution, just the lower part of the cake is immersed in liquid and "leaching" dissolves the active located in the upper part of the cake. Thus, one drawback to these cakes is that of the hypochlorite active in the uppermost part of the cake is wasted.
U.S. Pat. No. 4,208,747, Dirksing, issued June 24, 1980, discloses highly effective dispensers which are placed in a toilet tank and which receive a dose volume of water from the toilet tank and dispense a dose volume of a solution of cleaning or disinfecting composition every time the toilet is flushed. This patent teaches that cake compositions can be used as the source of cleaning and disinfecting agents in such dispensers, but fails to address specific problems posed by certain types of cakes. One problem is that a cake of calcium hypochlorite material immersed completely in the dosing liquid tends to initially deliver excessively high levels of chlorine. Thus, the chlorine is used up too fast. FIGS. 9-14 and 18 of U.S. Pat. No. 4,208,747, Dirksing, disclose "top-feed" dispensers in which such cakes are completely immersed in the dosing liquid. There, the solution is drawn from above the cake. Such cake/dispenser combinations do not deliver a consistent amount of available chlorine over the life of the cake. In contrast, the Dirksing '747 patent also discloses a dosing dispenser of the "bottom-feed" type illustrated in FIGS. 1-8 and 15-17. Symmetrical rectangular-shaped cakes are used therein. In such dispensers the bleach cake is only partially immersed in dosing liquid in the reservoir. The solution is drawn from an area near the bottom of the cake. This latter concept is important to the present invention.
U.S. Pat. No. 4,307,474, Choy, issued Dec. 29, 1981, discloses a passive dosing dispenser exhibiting improved resistance to gel clogging. An anti-clogging means comprising support means in the lowermost portion of the product chamber (cake compartment) and a level control means to control the level of liquid in the product chamber are also disclosed. The support means help to prevent gelled and solid chips from obstructing the flow of liquid in and out of the chamber.
Some major problems in this art have been with dissolving bleach cakes. One is dispensing even concentrations of the bleach. One cause of this is that particles from said cakes pass into the reservoir of the dispenser and thereby reduce the effective volume of liquid which is needed for rapid equilibrium and formation of the dosage of bleach which is to be dispensed in the next flush of the toilet. Further, the particles which break off the cake and pass through to the toilet water result in a loss of efficient bleach use, and some of the particles may clog the passageways through which liquid flows from the dispenser. Another problem has been that most of the effective volume of bleach liquid in the reservoir was dispensed with each dose.
It has recently been discovered that a filter sleeve can be employed in a "bottom feed" dispenser to retain the cake and chipped particles.
New problems in this art are related to the filter means material itself. The prior art preferred filter sleeves for solid cakes of hypochlorite are made from polyethylene and essentially pure polyester laid nonwoven fabrics. Delnet.RTM. nonwoven polyethylene P-5-30 and Novonette.RTM. Stock 149-305 polyester are some of the best prior art fabrics used as filter sleeve material. Experience with these materials employed in dosing dispensers revealed several things. First, dry storage problems were experienced after about six months. Second, polyester and polyethylene filter sleeves wick poorly. Thus, they have poor wetability, which impedes water contact with the cake and even hypochlorite delivery. Third, the Delnet and Novonette materials occasionally collapse, bunch or buckle when used in the dosing dispensers after some time. This may also impede even hypochlorite delivery. Fourth, these materials degrade in concentrated hypochlorite solutions.